The present invention relates to a method for generating and controlling the source of vacuum from a source of pressurized air to a vacuum responsive device, and more particularly, a method for maintaining the operating condition of a vacuum responsive device during the loss and resumption of power.
Vacuum operated work holding devices are commonly employed as workpiece gripping elements to engage and transport workpieces in a manufacturing operation, to load and unload sheet metal parts into and from a die, or to carry a part, such as an automobile windshield, to the vehicle in which it is to be installed. Such vacuum operated work holding devices employ a control apparatus which uses a venturi passageway and a body which is connected to a source of pressurized air. Airflow through the venturi passageway induces a sub-atmospheric pressure in the throat of the venturi and in a passage connecting the venturi throat to the interior of a vacuum operated work holding device, such as a vacuum cup. This sub-atmospheric pressure induces vacuum within the cup when the cup engages a workpiece surface.
Further advancements of the vacuum control apparatus have led to designs which generate and control a source of vacuum produced from a source of pressurized air that is positioned remote from the vacuum operated work holding device, thereby allowing for a single remote control system to control a plurality of vacuum operated work holding devices. These designs provide the distinct advantage of allowing a plurality of vacuum operated work holding devices to be attached to a single controller. This provides further flexibility as the vacuum flow rate available to the vacuum operated work holding devices can be increased by increasing the number of venturis engaged in the sub-atmospheric pressure generating system.
Due to the fact that these vacuum operated work holding devices are commonly utilized in an industrial environment, the power supplied to these devices is often interrupted. For example, such devices are often provided with emergency stops wherein an operator of the device may actuate the emergency stop to cut the power to the device. When this occurs, it is desirous to have the vacuum operated work holding device, such as a vacuum cup, maintain its vacuum so that any workpiece that is being held by the vacuum cup will be maintained and held by the vacuum cup. On the other hand, if the vacuum cups are not engaging a workpiece when the power is disengaged, then it is desirous to have the air supply disengage so that pressurized air is conserved.
Possible solutions to these problems include electrically wiring the vacuum operated work holding device prior to the emergency stop so that power will be maintained to the vacuum control apparatus even after power has been disengaged to the remainder of the system. This solution is typically not desirable since most operators do not wish for any power to be linked to the system in an emergency stop condition.
Another possible solution is to add a power failure override circuit to the vacuum operated work holding device so that the vacuum generating device runs at a maximum vacuum condition when the power is disengaged. The disadvantage with this system is that the vacuum will continue to run regardless of whether the vacuum cups are currently engaging a workpiece. This of course, fails to conserve pressurized air and fails to reduce the level of unnecessary noise caused by the continuous blowing of pressurized air.
It is desirable to provide a method that will maintain the operating condition of a vacuum responsive device during the loss and resumption of power.
The present invention overcomes the above-noted disadvantages by providing an improved method for generating and controlling the source of vacuum produced from a source of pressurized air in communication with at least one vacuum responsive device wherein the method maintains the operating conditions of the system during the loss and resumption of power. The method includes selectively providing a flow of pressurized air from the pressurized air source to a vacuum creating device. Vacuum is created by passing pressurized air through the vacuum creating device and communicating the vacuum to the vacuum responsive device. Vacuum is negated by selectively providing a flow of pressurized air from the pressurized air source to the vacuum responsive device. The method also includes maintaining the operating condition of the vacuum responsive device by selectively providing pressurized air to the vacuum creating device during the loss and resumption of power.
Vacuum is created by directing a flow of pressurized air through at least one venturi. More venturis may be added to increase the amount of vacuum applied to a vacuum responsive device or to increase the number of vacuum responsive devices utilized.
Pressurized air is selectively provided to the vacuum creating device by actuating a vacuum solenoid operated valve between an open position, wherein pressurized air flows through the vacuum solenoid operated valve from the pressurized air source, and a closed position, wherein pressurized air from the pressurized air source is blocked from flowing through the vacuum solenoid operated valve. An external power solenoid operated valve is actuated in a first position, wherein pressurized air from the vacuum solenoid operated valve flows through the external power solenoid operated valve, and deactuated in a second position, wherein pressurized air from the vacuum solenoid operated valve is blocked from passing through the external power solenoid operated valve. A vacuum pilot poppet valve is moveable between an open position, wherein pressurized air from the pressurized air source flows through the vacuum pilot poppet valve, and a closed position, wherein pressurized air is blocked from flowing through the vacuum pilot poppet valve. A vacuum poppet valve communicates with the vacuum pilot poppet valve and is communicatable with the pressurized air source. The vacuum poppet valve is movable between an open position, wherein pressurized air from the pressurized air source flows through the vacuum poppet valve to the vacuum responsive device, and a closed position, wherein pressurized air is blocked from flowing through the vacuum poppet valve.
Pressurized air is selectively provided to the vacuum responsive device by actuating a blow-off solenoid operated valve between an open position, wherein pressurized air flows through the blow-off solenoid operated valve from the pressurized air source, and a closed position, wherein pressurized air is blocked from passing through the blow-off solenoid operated valve. A blow-off poppet valve is movable between an open position, wherein pressurized air from the pressurized air source flows through the blow-off poppet valve to the vacuum responsive device, and a closed position, wherein pressurized air is blocked from flowing through the blow-off poppet valve.
Maintaining the operating condition of the vacuum responsive device includes moving a last function valve between an open position, wherein pressurized air from the vacuum solenoid operated valve moves the last function valve to an open position so that pressurized air from the pressurized air source may flow to the external power solenoid operated valve, and a closed position, wherein pressurized air from the blow-off solenoid operated valve moves the last function valve to a closed position so that pressurized air from the pressurized air source cannot flow through the last function valve. When power is lost to the solenoid operated valves and the vacuum responsive device is in the vacuum mode, the external power solenoid operated valve is deactuated to the second position, wherein pressurized air from the last function valve flows through the external power solenoid operated valve and is ultimately routed to the venturis to maintain vacuum during the loss and resumption of power. If power is lost to the solenoids during a blow-off condition, the last function valve remains in the closed position thereby preventing pressurized air from flowing to the vacuum generating means during the loss and resumption of power.
Sensing the level of vacuum being supplied to the vacuum responsive device is also provided. The level of vacuum is determined and sent to a controller after the loss and resumption of power. If the vacuum level is above a predetermined level, then the controller actuates the first valving means into a power-on vacuum mode. If the vacuum level is below the predetermined level, then the controller remains idle.